1. Field of the Invention
The present invention relates to a switching regulator circuit that converts an input voltage to a predetermined voltage by stepping up or by stepping down an input voltage.
2. Description of the Related Art
Certain switching regulator circuits can convert an input voltage to a predetermine voltage in a step-up operation or in a step-down operation. FIG. 1 illustrates circuitry of a related art step-up (booster)/step-down (buck) switching regulator (switch-mode power supply circuit) circuit 111, as disclosed in Japanese patent no. 3,787,785 (JP-3787785-B).
In FIG. 1, when the input voltage Vin is higher than an output voltage Vout, a switching regulator circuit 111 charges an inductor 110 via a switch 116 and discharges the inductor 110 via a switch 118 so that an output voltage Vout is set to a predetermined step-down value. In addition, when the input voltage Vin is lower than the output voltage Vout, the switching regulator circuit 111 charges the inductor 110 via a switch 136 and discharges the inductor 110 via a switch 134 so that the output voltage Vout is set to a predetermined step-up value. The switching regulator circuit 111 includes a prefix circuit 112, a step-up circuit 114, and a triangular wave generation circuit 30. The prefix circuit 112 includes a low pass filter (LPF) 130, an input terminal IN, and a control circuits 120 that includes a reference voltage generation circuits 124, an error amplification circuit 122, a pulse width modulation (PWM) comparator 126, and an inverters 128. The step-up circuit 114 includes an output terminal OUT, a smoothing capacitor Co, and a control circuit 138 that includes an error amplification circuit 140, a PWM comparator 142, and an inverter 143. The error amplification circuit 140 includes a resistor division circuit 144, a current output amplification circuit 146, an output circuit 148, and a reference voltage generation circuit 150.
The switching regulator circuit 111 shown in FIG. 1 adjusts the output voltage Vout to the predetermined voltage, regardless of the relative magnitudes of the input voltage Vin and the output voltage Vout. Therefore, the switching regulator 111 can adapt to both systems in which the input voltage Vin is higher than the output voltage Vout and those in which the input voltage Vin is lower than the output voltage Vout.
However, the switching regulator circuit 111 requires a switching circuit that automatically switches the step-up control and step-down control, therefore, the circuit size increases. In addition, the configuration of the control circuit becomes complicated.
Further, in the related-art step-up/step-down switching regulator circuit 111, because the switch 116 is provided in the path through which the current is supplied from an input terminal IN to which the input voltage Vin is inputted even though the switch 116 is not required in the step-up operation, a switching loss occurs in the switch 116. Similarly, because the switch 134 is provided in the path through which the current is supplied to an output terminal OUT from which the output voltage Vout is outputted even though the switch 134 is not required in the step-down operation, a switching loss occurs in the switch 134.
In view of the foregoing, there is market demand for a switching regulator circuit that can avoid reduction in switching conversion efficiency and has a simple configuration with the number of the elements in the entire circuit reduced.